To find creative common pictures go to Google and then images. Research the topic you need for your picture search.
Once you have done this, you should come across a page that looks similar to this. Press the ‘advanced search’ button (highlighted in the red box ) and it should take you to the image below.
Once at this page, there is an option for how you want Google to return your images. Click that option and then select the ‘labeled for commercial and reuse with modification’ (highlighted in the red box). Then press Google search and it will give you all the images on creative commons.